In die transfer systems of the subject character, a finger bar extends along one or both lateral sides of the die stations of a stamping press, and fingers extend inwardly from the finger bar or bars for engaging workpieces at the successive die stations. The finger bar or bars are driven longitudinally and laterally in synchronism with operation of the press for transferring workpieces through successive die stations and then out of the die. U.S. Pat. Nos. 4,032,018 and 5,307,666 each disclose die transfer systems of this general character, in which the finger bars are mechanically coupled by cam-and-follower arrangements to the ram of the stamping press for controlling operation of the finger bars.
It is a general object of the present invention to provide a die transfer system of the general type disclosed in the above-noted patents and discussed above, in which the transfer system as well as components thereof are of modular construction for providing enhanced flexibility in design and operation, and reduced inventory and maintenance costs. Another and more specific object of the present invention is to provide a die transfer system of the subject character in which the finger bar drive mechanisms are driven by electrically controlled servo motors for providing enhanced design flexibility in synchronizing operation of the transfer system to motion of the press ram.
A die transfer system for transferring workpieces between successive die stations in a stamping press includes an elongated finger bar having spaced fingers for engaging workpieces at successive die stations, a first drive mechanism for reciprocating the finger bar longitudinally for transferring workpieces between successive die stations, and a second drive mechanism for reciprocating the finger bar laterally into and out of engagement with the workpieces at the die stations. In accordance with the presently preferred embodiments of the invention, the second drive mechanism comprises at least two finger bar drive modules coupled to the finger bar and spaced from each other lengthwise of the finger bar. A drive shaft extends between and interconnects the two drive modules. Each of the drive modules includes a crank arm coupled to the drive shaft for rotating the crank arm about an axis parallel to the finger bar. A cam plate is coupled to the finger bar and mounted for movement lateral to the crank arm axis and the finger bar. The cam plate has a cam slot extending in a direction lateral to the crank arm axis, and a cam follower is mounted on the crank arm and disposed in the slot such that rotation of the drive shaft rotates the crank arm and propels the cam follower along the cam plate slot while simultaneously driving the cam plate and the finger bar laterally into and out of engagement with workpieces at the die stations. The drive shaft is rotated in synchronism with operation of the stamping press, preferably by an electric servo motor and motor controller coupled to a sensor for monitoring position of the stamping press ram.
The drive shaft in the preferred embodiments of the invention comprise a plurality of shaft segments each extending between and interconnecting an adjacent pair of the drive modules. Each drive module includes facility for interconnecting successive drive shaft segments so that all of the drive shaft segments and all of the finger bar drive modules operate in unison. Stub shafts are carried in each of the drive modules, and are interconnected by gears on the respective shafts. One of the stub shafts is connected to the crank arm of the associated module. The drive shaft segments that interconnect each module with the adjacent modules are connected by couplers to opposite ends of one of the stub shafts, or are connected to the ends of the respective stub shafts so that the two drive shaft segments are laterally offset from each other. Each of the finger bar drive modules preferably comprises a fixed support having a pocket in which the gears are disposed, and a cover plate enclosing the pocket. The cam plate is mounted on the support by a linear bearing arrangement for stabilizing operation of the cam plate.
In one embodiment of the invention, the cam plate has a single cam slot for providing lateral motion of the finger bar in only one direction and essentially shuttling workpieces in a plane from station to station in the stamping press. In another embodiment of the invention, the cam plate has first and second orthogonal interconnected cam slots, so that rotation of the drive shaft and crank arm propels the cam follower along the first and second slots in sequence, and thereby drives the cam plate and the finger bar sequentially in first and second directions at right angles to the crank arm axis and to each other. This embodiment thus implements three-direction motion of the finger bar to move the workpieces longitudinally between successive die stations, lower the workpieces onto the die stations, retract the finger bar and fingers laterally outwardly and rearwardly, and then propel the finger bars and fingers inwardly and then upwardly to lift the workpieces for a subsequent transfer operation. In such two-axis drive modules, a locking cam is operatively coupled to the drive shaft for corotation with the crank arm, and a locking cam follower is coupled to the cam plate. The locking cam has an arcuate surface that engages the locking cam follower during motion of the crank arm follower along the second cam plate slot to prevent the cam plate and the finger bar from reverse motion in the first direction during motion thereof in the second direction.
As noted above, the drive shaft that interconnects the finger bar drive modules preferably is coupled to an electric servo motor for operating the finger bar responsive to position of the stamping press ram. A sensor provides an electrical signal as a function of press ram position, and a motor controller has information prestored in memory coordinating desired finger bar position with sensed press position. This information is retrieved as a function of the press position signal, and the servo motor is operated accordingly to control position of the finger bar. This arrangement has the advantage of providing enhanced design and operating flexibility. For example, motion of the finger bar can be readily limited to less than full available motion of the crank arm and cam plate by simply reconfiguring the data prestored in the motor controller memory. In the same way, acceleration and velocity of the finger bar, and of workpieces engaged and carried by the finger bar, may be readily controlled and varied by reconfiguring the control information stored in the motor controller.
In the preferred embodiments of the invention, the finger bar is indexed longitudinally of the die stations by an electric servo motor coupled by an endless belt arrangement to the finger bars to reciprocate the finger bars back and forth with respect to the die stations. The indexing motor is controlled as a function of press ram position, providing the same enhanced design and operating flexibility discussed immediately above. The finger bar and drive arrangement may be employed singly or in pairs disposed on opposite sides of the die stations and mirror images of the other. Each finger bar and associated lateral drive mechanism, as well as the finger bar longitudinal indexing drive mechanism, preferably is mounted on an associated portable base plate as a modular assembly.